Galiy O. Influence of chemical and phase composition, as well as surface condition, on electrochemical properties of alloys ZrNiMnCrMe (Me = V, Al) and electrodes on their basis

It has been found that the metered oxidation of ZrNi1.2Mn0.5Cr0.2Ме0.1 (Me = V, Al) alloys when exposing in the air in the form of powders or pressed electrodes leads to accelerating the activation process and increasing cyclic stability under electrochemical saturation with hydrogen. It has been shown that exposure in the air positively affects the rate of activation of electrodes pressed from a powder of mechanically activated vanadium-containing alloy with additives of 10, 20 and 50 wt. % Ni. Impedance electrochemical spectroscopy has established that electrodes made of unoxidized and metered oxidized powders of the ZrNi1.2Mn0.5Cr0.2V0.1 alloy are characterized by various equivalent electrical circuits. In the case of the electrode made of unoxidized powder, a charge transfer is a limiting stage. The correlation is established between the cyclic stability of electrodes from ZrNi1.2Mn0.5Cr0.2Ме0.1 (Me = V, Al) alloys and their electrochemical stability at the potentiodynamic cycling in the cathode region. It means that the smaller the difference between cathode currents of direct and reverse stroke and their change from cycle to cycle during the first ten cycles, the higher the cyclic stability of the electrodes. Electrodes pressed from the air exposed powders of alloys exhibit the highest stability in potentiodynamic cycling. The electrode made of the ZrNi1.2Mn0.5Cr0.2Аl0.1 alloy powder air-exposed for 3 days has the highest stability in potentiodynamic cycling and at the same time the best cyclic stability. For 500 cycles of charge-discharge, the loss of discharge capacity by this electrode is only 25%, the electrode of unoxidized alloy powder loses 56% after 250 cycles. The conducted long-term potentiodynamic cycling (10 cycles) revealed the cause of the mismatch between the maximum activity of the freshly prepared electrode from the ZrNi1.2Mn0.5Cr0.2V0.1 alloy in the first cycle and its smallest maximum achieved discharge capacity. This cause is the loss of activity by the electrode during cycling. The electrodes, which during cycling most lose their activity, undergo the greatest mechanical destruction, and thus show the lowest cyclic stability. It was shown for the vanadium-containing alloy as an example that increasing the cyclic stability of the electrodes is facilitated by: use of shallow discharge to the potential difference E = −1,0 V; increase in the porosity of the electrodes; the preliminary stepwise air exposure of the alloy in the form of powder or ingot, reducing the size of air-exposed powder particles. The methods of atomic absorption spectroscopy and polarization curves has established that the preliminary exposure in the air of alloys ZrNi1.2Mn0.5Cr0.2Ме0.1 (Me = V, Al) leads to an increase in their corrosion resistance. By means of scanning electron microscopy it has been shown that the preliminary exposure in the air of the ZrNi1.2Mn0.5Cr0.2V0.1 alloy leads to an even distribution of smaller corrosive areas during its hydrogenation-dehydrogenation in comparison with such without preliminary exposure.